1. Field of the Invention
The present invention relates to a display panel. More particularly, the present invention relates to a filter which is attached to a plasma display panel, and a plasma display panel having the filter.
2. Description of the Related Art
In general, a plasma display panel (PDP) is a device that displays an image using electric discharge. Such a plasma display panel has become very popular because the plasma display panel has a superior display performance in luminance and viewing angle than other display devices.
The plasma display panel is classified into a facing discharge type and a surface discharge type depending on the arrangement of electrodes. In the facing discharge plasma display panel, a pair of sustaining electrodes is provided on upper and lower substrates, and discharge is generated in a vertical direction of the panel. On the other hand, in the surface discharge plasma display panel, a pair of sustaining electrodes is provided on one substrate, and an electric discharge occurs on the surface of the substrate.
Although it has a high luminous efficiency, the facing discharge plasma display panel has the disadvantage that phosphors easily deteriorate due to the electrical discharge. Recently, the surface discharge plasma display panel has been mainly used.
FIG. 1 is a view illustrating the construction of a general plasma display panel. The plasma display panel shown in FIG. 1 is a surface discharge plasma display panel. In order to easily illustrate the internal construction of the plasma display panel, a part of the plasma display panel is cut, and only an upper substrate 20 is rotated at right angle with respect to a lower substrate 10.
A plurality of address electrodes 11 are arranged in stripes on the upper surface of the lower substrate 10. The address electrodes 11 are embedded in a first dielectric layer 12 made of white dielectric material. A plurality of partitions 13 are provided at a predetermined interval on the upper surface of the first dielectric layer 12 in order to prevent electrical or optical crosstalk among discharge cells 15. A fluorescent layer 14 is coated on the inner surface of the respective discharge cells 15 defined by the partitions 13, and the discharge cells 15 are filled with a discharged gas which is generally a mixture of Ne and Xe, to generate the plasma discharge.
The upper substrate 20 is a transparent substrate, mainly made of glass, allowing visible light to pass. The upper substrate 20 is sealingly assembled to the lower substrate 10 with the partitions 13 formed thereon. On the lower surface of the upper substrate 20, pairs of sustaining electrodes 21a and 21b are provided in stripes in a direction perpendicular to the address electrodes 11. The sustaining electrodes 21a and 21b are made of transparent conductive material such as indium tin oxide (ITO). Bus electrodes 22a and 22b made of metal are provided on the lower surfaces of the sustaining electrodes 21a and 21b, so as to reduce line resistance thereof, and have a width narrower than that of the sustaining electrodes 21a and 21b. The sustaining electrodes 21a and 21b and the bus electrodes 22a and 22b are embedded in a second transparent dielectric layer 23. A protective layer 24 is formed on the lower surface of the second dielectric layer 23, and serves to prevent the second dielectric layer 23 from damage due to sputtering of plasma particles and also to reduce discharge voltage and sustaining voltage by emitting secondary electrons. The protective layer 24 is generally made of magnesium oxide (MgO).
A plurality of black stripes 30 are formed on the upper surface of the upper substrate 20 to prevent light from entering the interior of the plasma display panel from the outside of the panel. The black stripes 30 are formed parallel with the sustaining electrodes 21a and 21b at regular intervals.
With the above arrangement of the plasma display panel, the address discharge is generated between any one of the sustaining electrodes 21a and 21b and the address electrode 11. During this address discharge, wall charges are generated. Then, the sustaining discharge is generated due to the potential difference between the pair of sustaining electrodes 21a and 21b, and thus UV light is generated from the discharged gas. The fluorescent layer 14 is excited by the UV light to emit visible light. The visible light passing through the upper substrate 20 forms an image which can be seen by human eyes.
FIG. 2 is a graph illustrating an optical characteristic of a conventional plasma display panel.
FIG. 2 is a profile depicting a luminance distribution depending on a viewing angle β of the visible light emitted from the discharge cells 15. The visible light generated from the discharge cells 15 of the plasma display panel are diffused light emitted in all directions, and thus the luminance distribution of the diffused light is varied as a function of the viewing angle β.
In the conventional plasma display panel as described above, the external light enters the interior of the discharge cell 15 or is reflected from the upper substrate 20 under bright room conditions, and this causes a bright room to deteriorate the contrast. Further, since the visible light generated from the discharge cell 15 are diffused light having no uniform direction, as shown in FIG. 2, its transmittance deteriorates, and thus the screen display ability of the plasma display panel is depreciated.